Solvent treatments of textiles

ABSTRACT

IN THE DYEING OF TEXTILE SUBSTRATES BY THE ACTION OF A DYE LIQUOR COMPRISING A DYESTUFF HAVING AS A VEHICLE AN ORGANIC SOLVENT, A METHOD OF AND AN APPARATUS FOR, PERFORMING THE DYEING ON SUBSTRATE ARRANGED IN A A SEALED TREATMENT VESSEL AND FOR SUBSEQUENTLY REMOVING THE DYE LIQUOR FROM THE SUBSTRATE, WHILST THE LATTER REMAINS IN THE SAID VESSEL, BY THE PASSAGE OF STEAM THROUGH THE SUBSTRATE UNDER REDUCED PRESSURE.

Sept. 19, 1972 w. FURNESS 3,692,46

SOLVENT TREATMENTS 0F TEXTILES Filed Oct. 26. 1970 United States Patent Ofice 3,692,464 Patented Sept. 19, 1972 3,692,464 SOLVENT TREATMENTS F TEXTILES Will Furness, Thurnby, England, assignor to Samuel Pegg & Son Limited, Leicester, England Filed Oct. 26, 1970, Ser. No. 83,772 Int. Cl. B05c 8/02, 9/12 US. Cl. 8149.1 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to methods of, and apparatus for dyeing textile substrates by a so-called solvent dyeing process. By the term solvent dyeing, when used hereinafter, is meant a process in which use is made of a dye liquor which comprises a dispersion, emulsion or solution of dyestuif in an organic solvent.

The organic solvent is customarily a halogenated (preferably chlorinated) hydrocarbon, for example trichloroethylene, perchloroethylene, 1,l,ltrichloroethane, methylene chloride, 1,1,2-trichloro 1,2,2 trifiuoroethane, or mixtures thereof. The dyestuif is either dissolved in the solvent, or is dispersed therein either directly or in an emulsion with water. In any event the organic solvent provides a non-inflammable and volatile vehicle for the dyestuif.

Whilst the use of organic solvent as a vehicle does confer special advantages to a dyeing process, as compared with a similar process carried out using water as the vehicle, these solvents can be very harmful to any persons coming into contact with them while handling the dyed substrate. Thus it is desirable to remove as much of the solvent as possible after the dyeing stage of the process. Furthermore it is desirable to recover the organic solvent so that it may be re-used; clearly this reduces the cost of the process.

One previous technique for drying the dyed substrate and recovering organic solvent from the process has comprised subjecting the dyed substrate to the action of steam. The steam initially condenses on the substrate, forming an azeotrope with the solvent which azeotrope 'boils at a lower temperature than either the solvent or water. The steam then provides heat for evaporation of this azeotrope and the resulting vapour is drawn by means of a fan to a condenser. One drawback to this technique is that the temperature of the steam, which is normally over 100 C., is sufiiciently high to cause migration of dyestuff taken up by the substrate. This is particularly the case where the substrate is of appreciable thickness. In order to overcome this drawback it has been proposed that the steam of this technique be replaced by hot air. This prevents the said migration of the dyestuff, but the technique requires a very great volume of air, as compared with steam, and at a temperature which is sulficient to raise the organic solvent itself to its boiling point; this temperature is sufiicient with certain solvents to damage some types of textile. The air must then be cooled and passed through a far more complex condenser or, e.g. an activated charcoal separator, if the solvent is to be successfully recovered. Furthermore, for the successful removal of solvent where the textile is of any appreciable thickness an excessively long exposure to hot air is required.

For these reasons solvent dyeing has, generally speaking, previously only been applied to continuous processes. That is to say, to processes in which a textile substrate in the form of a woven fabric or a plurality of spun threads is passed through a bath containing a solvent dye and thence to an extraction chamber where it is subjected to steam and the resulting vapour is extracted for condensation of the organic solvent. In this process the substrate is of relatively small thickness, i.e. a web of fabric or a single thread respectively, and the effects of steam on the dyestulf are relatively small since the temperature of the substrate is raised substantially uniformly throughout its section. However, such a process must be performed in an enclosed apparatus in order to minimise the risk of volatile solvent vapour escaping and such an apparatus is complicated by the necessity for the substrate to be moved continuously therethrough.

An object of the present invention is to provide a method of, and an apparatus for, performing solvent dyeing which overcomes the aforementioned drawbacks.

According to the present invention a method of solvent dyeing a textile substrate in which the substrate is arranged in a treatment vessel, is subjected to a dyeing stage in which it is acted upon by a batch of dye liquor which is passed repeatedly through the vessel and through the substrate, and to a drying stage in which the pressure in the vessel is reduced by the withdrawal therefrom of air and vapour through the textile substrate and steam is admitted into the vessel and is drawn through the textile substrate so as to remove the organic solvent by evaporation under reduced pressure.

The method of the invention provides improvements over known methods of solvent dyeing. For example, firstly, because the textile substrate remains arranged in the sealed vessel until it has been dried, the dangers of solvent vapour escaping are obviated; this arrangement of the substrate also overcomes the problems, inherent in a continuous process of conveying the substrate from dye bath to drying chamber etc. Secondly the dyeing is improved because the lower steam temperatures utilized, coupled with the drawing of the steam through the substrate, permits the practically complete drying of the substrate without any substantial risks of dye migration.

During the drying stage air may be periodically admitted to the vessel so as to purge it of steam and solvent vapour which is therefore swept out of the vessel by virtue of the reduced pressure.

The method of the invention is applicable to a wide range of textile materials, to be comprehended within the term substrates. For example, the substrate may be in loose form, eg as loose stock, tow, tops, muffs, or made up garments, it can be packed into suitably formed baskets so shaped that they can be mounted in the vessel and define a path, through substrate packed therein, for solvent dye liquor and steam. Alternatively made-up garments could be mounted on appropriately shaped formers. It may be in the form of fabric and wound on a beam, or it may be in the form of yarn wound on cheeses, bobbins, cones or beams. In these cases it is either arranged that the beams or cheeses etc. guide the dye liquor and the steam through the substrate, or the beams or cheeses, etc. are held in suitable carriers to achieve the desired result. For example, the fabric or packages can be disposed on a perforated carrier into which the solvent dye liquor is passed.

The dyeing stage may be performed at any temperature between room temperature and C. depending on the particular properties of the dyestutf and of the textile substrate.

When the temperature is raised to above the normal boiling point of the solvent it may be necessary to pressurise the vessel. This may be done either by admitting air under pressure or by the action of a secondary pump against an orifice plate. The pressure is raised to avoid vapourisatio-n of the solvent or any azeotrope formed in an emulsion or solution dye liquor and to obviate cavitation in the circulating pump.

Solvent dye liquor remaining free in the vessel after the dyeing stage is preferably removed before the drying stage, but after a cooling stage, if the dyeing stage has been performed with heated liquor. This cooled liquor may be allowed to drain into a catch tank, it may be drawn off by means of a suction pump or it may be blown from the tank by the action of compressed air.

It is not essential for the drying stage to follow immediately on the dyeing stage. It may, for example, be de sirable to submit the substrate to an intermediate rinsing stage in which the same solvent, either alone or with a cleaning agent, a fixing agent or a softening or other agent, is passed through the vessel and through the substrate. Furthermore the substrate may be washed in the vessel before the dyeing stage, if this is desired.

An apparatus for performing the method of the invention comprises essentially a single sealable treatment vessel, a liquid pump connected with the vessel in a circulation path for dye liquor through the vessel and the pump. A vacuum pump has its suction inlet connected with the vessel and its outlet connected with a reservoir for organic solvent. Steam is admitted into the vessel when required through an inlet and the substrate is mounted on a carrier in the vessel in such a manner as to be interposed both in the said circulation path for dye liquor and between the inlet for steam and the suction inlet of the vacuum pump.

The vacuum pump is preferably of the liquid ring type and the seal between the pump casing and the pump vanes is provided by liquid solvent condensed from the vapours drawn from the vessel. This arrangement has been found to give advantages as compared with when the pump is sealed in the conventional manner by water or oil. The mixture of vapour and condensate is discharged by the pump into the solvent reservoir at a small positive pressure where the condensation of the solvent is completed.

It has been found that at a pressure of around the range of 22 to 26 inches of mercury the steam condenses on the textile substrate to form an azeotrope with the solvent which evaporates at a temperature at which migration of dyestuff is negligible. However the invention is not limited to this range of pressures. By drawing the vacuum on one side of the substrate and supplying the steam at the other a rapid rate of steam flow at reduced pressure through the substrate is achieved.

One specific way of performing the method of this invention will now be described with reference to the accompanying drawing which illustrates a form of plant for this purpose.

Thus the textile substrate which, in the drawing is represented by yarn wound on a plurality of bobbins 1, is mounted inside an upright cylindrical treatment vessel 2 having a pressure-tight lid 3.

The bobbins 1 are mounted on vertical perforated hollow posts 4 spaced apart around the periphery of a circular carrier or header pipe 5. The posts 4 are so arranged that the bobbins I mounted thereon form one or a number of coaxial annular series of stacks around the carrier 5. Each stack of bobbins is secured to its post by butterfly nuts 6 which also serves to secure atop plate (not shown) which closes the top of the stack of bobbins. Alternatively each top plate could be held down by a weight or spring; such an arrangement would ensure that the top plate remained in position in the event of the yarn shrinking. The annular carrier plate is mounted in the vessel in communication with the upper end of a central pipe 7 which passes through the bottom wall of the vessel to a centrifugal liquid circulating pump 8. A second pipe 9 connects the pump 8 with the lower part of the vessel 2. This second pipe is provided with a valve 10.

Valve-controlled inlets 1'1 and 12 in the side wall of the vessel connect the latter with a steam or air supply and a clean solvent supply respectively. A heating coil 13 is mounted in the vessel 2 around the pipe 7. This coil also serves as a cooling coil after the dyeing stage.

The liquid circulating pump 8, in addition to forming a part of a circulating system for dye liquor, also provides a passage from this circuit to a solvent recovery circuit. To this end the pump 8 is provided with an outlet pipe 14 which divides into two arms '15 and 16 having control valves 17 and 18 respectively. The first of these arms 15 connects directly with a catch tank 19 for spent dye liquor and the second, 16, connects with the inlet of a liquid ring vacuum pipe 10 by way of a spray condenser 21. The outlet of the vacuum pump 21 connects with a solvent reservoir 22 by Way of a pipe 23. This reservoir is provided with a cooling coil 24, a vent valve 25. A service pump 27 is also connected to the reservoir 22 by way of an inlet pipe 26; this pump is connected to the spray condenser 21.

Whilst the carrier 5 and the posts 4 would be used in the treatment of bobbins, spools or cheeses of textile substrate, i.e. yarn, they would not be suitable for the treatment of loose stock or made up garments. For this purpose either of two forms of basket could be utilised. One of these forms of basket consists of a lower end plate of annular form adapted to fit onto the central pipe 7. A central perforate pipe passes along the axis of the basket and is secured at its upper end to a circular top end plate. This top end plate is removably secured to a cylindrical perforate wall of the basket. The textile substrate to be treated is packed in the basket in the annular space between the wall and the perforate central pipe.

The second basket consists of a plain annular lower end plate, a false perforate bottom above the annular lower end plate, an imperforate cylindrical wall and a removable perforate upper circular end plate. The substrate to be treated is packed in this basket in the cylindrical chamber defined by the false bottom, the cylindrical wall and the upper end plate.

When performing the dyeing stage a batch of dye liquor is introduced into the pressure treatment vessel 2 through the inlet 12, the vessel is pressurised by the admission of compressed air through the inlet 11, and the liquor is circulated for a predetermined length of time by the liquid pump 8, whilst being heated by the coils 13 which are being supplied with steam at this time. The path of circulation is as follows; over the heater coils 13, and to the pump by way of the inlet 9; through the pump; back to the interior of each of the stacks of bobbins 1 by way of the hollow parts 4; outwards through the yarn wound on these bobbins, and back to the pump to repeat the circuit. Thus throughout a dyeing stage, dye liquor is forced under pressure from the pump 8, radially outwardly through each stack of bobbins 1. The circulation may advantageously be reversed at intervals throughout the dyeing stage. This is achieved by reversing the pump 8, e.g. by means of a change over valve, and results in the dye liquor passing inwardly through the substrate. It should be noted the maximum pressure in the vessel during the dyeing stage is reduced to a safe value by the provision of an expansion tank (not shown). This tank which is connected to the vessel 2, accepts the increased volume of liquid which results from the thermal expansion of the latter.

At the end of the dyeing stage the pump 8 is de-energised, the supply of steam to the coils 13 is cut olf and water is circulated through these coils to cool the heated dye liquor. When the dye liquor is sufiiciently cooled the valve 17 is opened and compressed air is admitted through the inlet 11, thereby causing the used dye liquor in the vessel 2 and in the pump 8 to drain into the tank 19.

When draining is completed there may be a rinsing stage which is performed in precisely the same manner as the dyening stage described but with dyestutf-free sol-vent.

The textile substrate is then dried by the action of steam at reduced pressure. To achieve this the valves and 17 are closed, the valve 18 is opened and the vacuum pump 20 and the service pump 27 are energised; the latter withdraws solvent from the reservoir 22 and forces it into the spray condenser 21 where it condenses the solvent vapour withdrawn from the vessel 2. The liquid solvent thus formed is drawn into the vacuum pump 20 where it provides a liquid ring seal for the vanes. Thus any vapourised solvent and air in the vessel together with a certain amount of used dye liquor contained in the textile substrate is withdrawn through the pipe 7 as the pressure is reduced.

When the pressure in the vessel has been sufliciently reduced, steam is admitted thereto through the inlet 11. Because the steam is supplied to the outside of the stacks of bobbins 1 whilst the vacuum is applied to the centre of each of these stacks the steam is speedily drawn through each stack thereby coming into intimate contact with every portion of the textile substrate, i.e. the yarn wound on the bobbins 1. The steam initially condenses on the textile substrate to form an azeotrope which would evapo rate at 87.7 C. at normal atmospheric pressure. However, by virtue of the reduced pressure in the vessel this evaporation temperature is reduced still further. The admission of steam to the vessel is controlled throughout the drying phase so as to maintain the temperature in the vessel as close as possible to the reduced evaporation temperature. As a result the azeotrope is evaporated and is drawn through the pipe 7 and the condenser 21, where it is at least partially condensed by the pump 20 which then forces the mixture of condensed solvent, water and vapour to the reservoir 22 where it is cooled by the coils 24 thus completing the condensation.

Periodically throughout the drying stage the supply of steam to the vessel is cut off and air is admitted thereto through the inlet 11. This supply of air has the effect of purging the vessel of steam and solvent vapours; in addition it causes the pressure in the vessel to rise to some extent and promote the purging action.

It is not essential to the method of the invention that the steam is drawn radially inwardly through an annular stack or pack of textile substrate. It could be for example, equally well be drawn radially outwardly; the apparatus in the drawing could be modified to achieve this by connecting the inlet 11 to the centre of the stack of bobbins 1 and by reducing the pressure through the pipe 9, the pipe 7 being closed by a valve. Furthermore the textile substrate could be arranged in other ways, for example, in the second basket described for use with this apparatus, the steam would be drawn axially through the cylindrical pack of substrate.

The solvent drawn oil and collected in the reservoir is not pure; firstly it contains the condensed steam, i.e. water; secondly a quantity of dye stulf which has not been taken up by the substrate but has been left therein is normally carried over by the steam and vapour as it passed therethrough. For these reasons it is necessary to re-purify the solvent, eg by distillation before it can be re-used.

One specific example of the method of the invention is given herebelow:

500 grammes of nylon 66 continuous filament yarn was wound in the form of a cheese on a dyeing spring which weighed 79 grammes.

The dyestutf used was a commercial sample of a 2:1 metal complex acid dye (which is sold under the RTM Lanasyn Grey BL 250% This dye is also defined as CI Acid Black 58 in the Colour Index, 2nd edition, 1957 (published by The Society of Dyers and Colourists, Bradford, England, and the American Association of Textile Chemists and Colourists, Lowell, Mass, U.S.A.) The quantity of dyestuif used was 0.4% calculated on the weight of nylon.

The nylon was placed in the vessel and was pre-washed by circulating 7000 cc. of perchloroethylene therethrough for 8 minutes, this raising the temperature to 50 C.

The dye liquor was prepared by dissolving 2 grammes of the dyestufi' in 75 cc. of water at 60 C. together with 75 grammes of a non ionactive surface agent sold under the RTM Sovatex N /z which was stirred into the solution. The whole was then stirred into 350 cc. of cold perchloroethylene to form an emulsion of the water insolvent type.

This emulsion was then added to the 7000 cc. of perchloroethylene in the vessel and the resulting liquor was circulated for 5 minutes at 50 C.

The vessel was then closed, pressurised to 20 lb./in. and steam was admitted to the heating coils 13. Whilst the liquor was being circulated the temperature was raised to C. over a 20 minutes period and then held at this level for a further 20 minutes. At this time the dyeing stage was completed, this being indicated by the fact that the dye liquor was substantially free from colour.

The liquor was then cooled to 70 C. over a periodof 10 minutes and the pump 8 was de-energised.

Compressed air was then used to cause the liquor to drain into the catch tank. After draining the yarn was rinsed for 10 minutes at 50 C. with 6000 cc. of perchloroethylene into which 75 cc. of water dispersed with the aid of 77 cc. of Sovatex N /2 (RTM). This rinsing liquid was then drained into the catch tank by compressed arr.

During the subsequent drying stage the vessel was evacuated to around 26 in mercury by the vacuum pump. Steam from a 5 lb./in. static gauge pressure main was admitted to the outside of the yarn package over a period of 5 minutes during which time the temperature, as indicated by a thermistor situated inside the vessel adjacent the yarn package and measured by means of a Wheatstone bridge rose to 70 C. The flow of steam was then interrupted and air was admitted until the condensed vapour was seen to stop flowing through a sight glass. The vacuum had then dropped to 5 in mercury gauge pressure although the pump had continued to run. The air was turned off and the vacuum allowed to build up once more to 26 in mercury.

The cycle of steam and air flow, while maintaining the vacuum, was repeated twice more, whereupon it was noted that the condensed vapour contained no gloubles of perchloroethylene as they flowed through the sight glass. This took a total of 23 minutes from first evacuating the system. The vacum pump was then de-energised and air admitted to the machine to bring it to atmospheric pressure, the lid was opened and the nylon package removed. It was found to be free from the odour of perchloroethylene and, with its spring, weighed 682 grammes. That is to say, it contained 103 grammes Water or 20.1% of moisture calculated on the weight of nylon.

I claim:

1. A method for the dyeing of a textile substrate by action thereon of a dye liquor comprising a dyestuif having as a vehicle a liquid organic solvent, the latter being subsequently removed from the substrate by evaporation under the application of steam wherein the improvement comprises the steps of arranging the substrate in a sealable treatment vessel between an inlet and outlet of the said vessel, whereby the substrate is interposed in a liquid path between said inlet and outlet, Washing the substrate by passing an organic solvent repeatedly through the vessel and through the substrate, adding a dyestufi in emulsion, dispersion or solution with said organic solvent to the solvent in the said vessel so as to form a batch of dye liquor, closing the vessel, raising the pressure and temperature of the said dye liquor for a predetermined length of time which is sufiicient to dye the substrate, cooling the use dye liquor in the vessel, draining used liquor from the vessel, withdrawing air and vapour from the vessel through said inlet thereby to reduce the pressure in the vessel, and admitting steam into the vessel whilst under reduced pressure, the steam being drawn through said substrate and from the vessel through said inlet thereby removing the solvent by evaporation under reduced pressure.

2. A method according to claim 1 in which the removal of air and vapour from the vessel is efiected by a liquid ring pump, wherein the method further comprises the step of forming a liquid ring seal in the pump by condensing vapour from the vessel in the pump body.

3. A method for the dyeing of a textile substrate by action thereon of a dye liquor comprising a dyestuff having as a vehicle a liquid organic solvent, the latter being subsequently removed from the substrate by evaporation under the application of steam, wherein the improvement comprises arranging the textile substrate in a treatment vessel subjecting the said substate to a dyeing stage in which it is acted upon by a batch of the dye liquor which is passed repeatedly through the vessel and through the substrate and to a drying stage in which the pressure in the vessel is reduced by the withdrawal therefrom of air and vapour through the textile substrate and steam is admitted into the vessel and drawn through the textile substrate so as to remove this organic solvent by evaporation under reduced pressure, said admission of steam being interrupted at intervals during the drying stage and air is admitted into the vessel during said intervals so as to purge the vessel of steam and vapour.

4. A method for the dyeing of a textile substrate by action thereon of a dye liquor comprising a dyestutf having as a vehicle a liquid organic solvent, the latter being subsequently removed from the substrate by evaporation under the application of steam, wherein the improvement comprises arranging the textile sunbstrate in a treatment vessel, subjecting the said substrate to a dyeing stage in which it is acted upon by a batch of the dye liquor which is passed repeatedly through the vessel and through the substrate, subjecting the substrate to a rinsing stage by the action of dyestuif free solvent in said treatment vemel after the said dyeing stage and then subjecting said rinsed substrate to a drying stage in which the pressure in the vessel is reduced by the withdrawal therefrom of air and vapour through the textile substrate and steam is admitted into the vessel and drawn through the textile substrate so as to remove the organic solvent by evaporation under the reduced pressure.

References Cited UNITED STATES PATENTS 3,551,189 12/1970 Gray et al. 68-18 C 3,087,322 4/1963 Bahlo 68-189 509,431 11/1893 Graemiger 68-489 WILLIAM 1. PRICE, Primary Examiner US. Cl. XJR. 

